docs: def grow(self, thing):
          """Make the list longer, appending for unicode, extending otherwise."""
          if type(thing) == str_class:
              self.append(thing)
  
          # This will only ever match in Python 2 since str_class is str in
          # Python 3.
          elif type(thing) == str:
              self.append(unicode(thing))  # noqa: F821 undefined name 'unicode'
  
          else:
              # Recursively expand to a flat list; may deserve a C accelerator at
              # some point.
              for element in thing:
                  self.grow(element)